Characterization of the non-adrenergic/non-cholinergic response to perivascular nerve stimulation in the double-perfused mesenteric bed of the mouse

BACKGROUND AND PURPOSE

Calcitonin gene-related peptide (CGRP), a capsaicin-sensitive neuromodulator of splanchnic vascular tone in several animal species, remains poorly investigated in mouse models. We therefore assessed whether endogenous CGRP is a non-adrenergic/non-cholinergic (NANC) neuromodulator in the mesenteric vascular bed of the mouse.

EXPERIMENTAL APPROACH

Arterial and venous changes in perfusion pressure in response to perivascular nerve stimulation (PNS) were monitored in the mouse mesenteric bed under basal conditions or precontracted with KCl (artery) or U46619 (vein) in circuits pretreated with guanethidine, atropine, indomethacin and prazosin. Arterial responses to NANC were also characterized with a CGRP1 antagonist, halphaCGRP8-37. Finally, the PNS-induced release of arterial CGRP was measured by enzyme immunoassay.

KEY RESULTS

HalphaCGRP8-37 enhanced PNS-induced arterial increases in perfusion pressure under basal tone. PNS-induced stimulation of NANC triggered an halphaCGRP8-37 or capsaicin- sensitive reduction in perfusion pressure of the pre-contracted arterial bed only. Chemical removal of the endothelium inhibited PNS- and halphaCGRP- induced reduction in perfusion pressure in the arterial mesenteric bed. Responses to NANC nerves were reduced by guanylate and adenylate cyclase inhibitors (1H-[1,2,4]oxadiazole[4,3-a] quinoxalin-1-one (ODQ)) and [9-(tetrahydro-2-furanyl)-9H-purin-6-amine] (SQ 22,536), respectively. A neuronal NOS inhibitor (7-nitroindazole; 7-NI) also enhanced the response to NANC in vessels from wild-type, eNOS KO but not iNOS KO mice. Finally, PNS enhanced the release of immunoreactive CGRP from the perfused arterial mesenteric bed.

CONCLUSIONS AND IMPLICATIONS

Our study demonstrates a role for CGRP in the NANC-dependent reduction in perfusion pressure of the arterial but not venous mesenteric bed of the mouse.

Rho-kinase expression and its contribution to the control of perfusion pressure in the isolated rat mesenteric vascular bed

Rho-kinase expression was investigated in the rat mesenteric artery and the effects of its inhibitors, (+)-(R)-trans-4-(1-aminoethyl)-N-(4-pyridyl) cyclohexanecarboxamide dihydrochloride monohydrate (Y-27632) and fasudil (HA-1077), were examined on the increase in perfusion pressure induced by two different receptor agonists, namely the alpha-adrenoceptor agonist, phenylephrine and, the endothelin ET(A) and ET(B) receptor agonist, endothelin-1. Y-27632 and fasudil produced a concentration-dependent decrease in perfusion pressure. There was no difference between the concentration-response lines of these two inhibitors. The maximum decrease in the perfusion pressure induced by 10(-5) M Y-27632 was 85.8+/-3.7% when the tone was increased by phenylephrine. However, it was 48.1+/-5.4% (P<0.001) when the perfusion pressure was elevated by endothelin-1. Saponin perfusion (100 mg l(-1), for 10 min), which abolished acetylcholine-induced relaxation, did not significantly modify the Y-27632-elicited relaxation. Western blot analysis revealed that rat mesenteric artery expresses Rho-kinase protein with a molecular weight of approximately 160 kDa. These results show that Rho-kinase enzyme is expressed in rat mesenteric artery and that it contributes to the control of vascular resistance. Moreover, endothelium removal had no marked effect on the vasodilatation induced by Y-27632. In addition, the endothelin-1-induced vasoconstriction was more resistant to the Rho-kinase inhibitors than was that induced by phenylephrine, probably because excitatory endothelin receptors are associated with this signal transduction pathway at a different level from that of alpha-adrenoceptors.

Pharmacology of kinins in the arterial and venous mesenteric bed of normal and B2 knockout transgenic mice

We have tested the vasoactive effects of kinins in addition to various other endothelium-dependent or independent agonists in the arterial and venous perfused mesenteric circuits of the mouse. Bradykinin (0.1 pmol-100 nmol), but not des-Arg9-bradykinin (10 nmol) induced a dose-dependent vasodilation of the precontracted arterial and venous mesenteric vasculature of the mouse. Furthermore, acetylcholine (2.5 nmol) also induced a marked arterial vasodilation but was without effect on the venous side. Other endothelium-dependent vasodilators, such as platelet-activating factor (PAF) (1 nmol), tachykinin NK1 selective agonist ([Sar9,Met(O2)(l1) ]substance P) (0.5 nmol) and adenosine diphosphate (5 nmol), were without effect on either side of the mesenteric bed of the mouse. The bradykinin B2 receptor selective antagonist (HOE 140) abolished the arterial and venous vasodilation induced by bradykinin without affecting that of acetylcholine or sodium nitroprusside. In addition, the bradykinin B1 receptor antagonist des-Arg9-[Leu8]bradykinin was without effect on the responses induced by bradykinin. A nitric oxide synthase inhibitor N(omega)-nitro-L-arginine methyl ester (L-NAME) markedly reduced, whereas removal of the endothelium with 3-[3-cholamidopropyl)dimethylammonio]-1-propane sulfonate (CHAPS) abolished dilatation to bradykinin and acetylcholine (arterial side only) without affecting that induced by sodium nitroprusside in the mouse arterial and venous mesenteric circuits. In the same two circuits of transgenic B2 knockout mice, the vasodilatory responses to bradykinin were absent, whereas the arterial circuit still responded to acetylcholine by a L-NAME-sensitive vasodilation. Our results suggest the exclusive contribution of B2 receptors located on the endothelium in the vasodilatory effects of bradykinin in the arterial and venous mesenteric circuits of the mouse.